Method for washing filter and method for desalinating seawater

A seawater desalination method, comprising:

• a seawater desalination process, comprising:
• a first filtration in which seawater is micro-filtered or ultra-filtered, and
• a second filtration in which a reverse osmosis treatment is performed on seawater after the first filtration;
• and
• a filter cleaning process in which a filter used in the seawater desalination process is cleaned, wherein
• the seawater contains an inorganic compound comprising alkali metal or alkali earth metal,
• the filter is a microfiltration membrane or ultrafiltration membrane used in the first filtration,
• an iron compound is added to seawater during any stage of the desalination method,
• the cleaning process comprises:
• a cleaning solution preparation in which a cleaning solution is prepared, and
• a deposit removal in which deposits on the filter are removed by contacting the filter and the cleaning solution, and
• in the cleaning solution preparation, the cleaning solution is prepared by mixing a hydroxy dicarboxylic acid with the seawater after the first filtration and by mixing at least hydrogen peroxide with the seawater after the first filtration so that an initial iron compound concentration of the cleaning solution is within an initial range of 14.3 mmol/L to 37.9 mmol/L in terms of iron atoms, and adding additional iron compound such that a final iron compound concentration at the end of cleaning is within a final range of 19.8 mmol/L to 43.4 mmol/L;
• and
• performing the deposit removal via a filtration cleaning method,
• in the deposit removal, continuously or periodically carrying out measurement of the concentration of iron compound in the cleaning solution, and
• obtaining a measurement value of the iron compound concentration and adding the additional iron compound to the cleaning solution such that the iron compound concentration increases from the initial range.

A seawater desalination method, comprising:

• a seawater desalination process, comprising:
• a first filtration in which seawater is micro-filtered or ultra-filtered, and
• a second filtration in which a reverse osmosis treatment is performed on seawater after the first filtration;
• and
• a filter cleaning process in which a filter used in the seawater desalination process is cleaned, wherein
• the seawater contains an inorganic compound comprising alkali metal or alkali earth metal,
• the filter is a microfiltration membrane or ultrafiltration membrane used in the first filtration,
• an iron compound is added to seawater during any stage of the desalination method,
• the cleaning process comprises:
• a cleaning solution preparation in which a cleaning solution is prepared, and
• a deposit removal in which deposits on the filter are removed by contacting the filter and the cleaning solution, and
• in the cleaning solution preparation, the cleaning solution is prepared by mixing a hydroxy dicarboxylic acid with the seawater after the first filtration and by mixing at least hydrogen peroxide with the seawater after the first filtration so that an initial iron compound concentration of the cleaning solution is within an initial range of 14.3 mmol/L to 37.9 mmol/L in terms of iron atoms, and adding additional iron compound such that a final iron compound concentration at the end of cleaning is within a final range of 19.8 mmol/L to 43.4 mmol/L;
• and
• performing the deposit removal via an immersion cleaning method,
• in the deposit removal, continuously or periodically carrying out measurement of the concentration of iron compound in the cleaning solution, and
• obtaining a measurement value of the iron compound concentration and adding the additional iron compound to the cleaning solution such that the iron compound concentration increases from the initial range.